Advanced — Kepler from Circular OrbitHardQuestion 30672
Question
Deriving Kepler's third law from circular orbit: if v = √(GM/r) and T = 2πr/v, then T ∝:
- Ar^(1/2)
- Br^(3/2)Correct
- Cr²
- Dr^(2/3)
Correct answer
r^(3/2)
Explanation
T = 2πr/v = 2πr/√(GM/r) = 2πr×√(r/GM) = 2π√(r³/GM). So T ∝ r^(3/2), confirming Kepler's third law.